C5 Alternater ok / not ok?

[Argos69]

After a few months of "challenges" courtesy of our C5 2.2HDi Tourer, we have had a quiet time. Until now....

I borrowed a USB charger and plugged it in to the lighter socket on the centre console. It has a voltage display, which I started watching (as a passenger, I may add!). It cycled from 12.2V to 13v-14v and sometimes 14.5v. But, for the most part, it sits around 12.3-12.4v.

My thoughts are, that its too low / inconsistent.

I tried a decent voltmeter, plugged in to the diagnostic socket and low and behold, it's exactly the same!

I checked the battery state - looks ok, 12.37v dc when engine off. Checked the alternator belt - ok and using a Clarke charging systems tester, it says the alternator is "healthy".

So...... Is it an issue or not? The one thing I would say, is that every few months, the old tailgate issue crops up until I put the battery charger on for a day. but it always starts enthusiastically.

Thoughts folks?

[xantia_v6]

It is just the way they work.

The alternator output is controlled by the ECU, if it thinks the battery is not fully charged it sets the voltage at 14V, but if the battery is thought to be fully charged, it reduces the voltage to about 12.2 volts and exactly matches the electrical load (if you turn on the A/C or heated rear window the alternator will work harder but the voltage doesn't change).

This prevents the battery from being overcharged and probably saves fuel, but when the battery gets older, the system can wrongly estimate the battery state of charge, reducing the useful life of the battery.

[wurlycorner]

Yep, they're far more sensitively controlled these days - not like on an older car where it would be ~12v with engine off and ~14v with engine running.
As long as yours is staying above 12v and not giving you fault messages about not charging, then it's probably working ok.

[Argos69]

Thanks folks,

Just out of curiosity, I charged the battery fully, then today went for a drive. The voltage sat at 13.2-13.4 the whole time. No ups n downs.
So, I'm ok about it. My mate said "tape over the voltage display and forget about it". Maybe there's some sense in that?"

Thanks again

[shtu]

If you want to be certain the alternator is OK, unplug the small, probably single-wire, connector at the alterantor. You can see it below the large nut on this image as an example of where you are looking for it, https://files.ekmcdn.com/thestartermot/ ... 27bc0f2677

A small right-angle pick is quite handy to unclip that connector.

That will remove the ecu control of the alternator, and it defaults to full output.

Note - this will give a selection of stored error codes relating to the alternator, but no dash lights or anything, so it's a bit of a non-problem as long as you remember why they are there.

[Argos69]

Thank you for that. Very handy hint. I may try that at some point.

Been out in the car today 13.8 engine running, 12.4 engine off. I think I'm happy now.

Have a nice weekend.